Magnetohydrodynamic (MHD) power involves a system for directly generating electrical energy from an electrically conducting fluid such as an ionized gas as it passes through a magnetic field. The MHD system typically comprises a channel through which ionized gas flows and a magnetic field that is transverse to the axial flow of the gas. It has been determined that in order to efficiently and economically operate such a system magnetic fields of at least from 3 to 7 Weber/meter.sup.2 are desirable. In order to obtain such magnetic fields the use of superconducting magnets (those cooled to about 4.degree. K. ) are necessary (Z. J. J. Stekly and R. J. Thome, Proceedings of the IEEE, Volume 61, 1973, pages 85-95).
In order to generate a magnetic field of the required strength in a transverse direction to the flowing gas the use of magnet windings which are longitudinal, that is parallel to the MHD channel and which cross over at each end of the MHD channel are required. This configuration is achieved either by the use of flat racetrack-shaped windings or saddle-shaped windings in which the end turns are arched to clear the MHD channel. Normally such a magnet includes halves which are mirror images of each other and are to form a bore in which the MHD channel is located.
Each of the individual conductor turns is provided with electrical insulation and it is desirable that it is constructed so as to minimize relative movement of the individual conductor turns under the action of the magnetic loads. If relative motion occurs between adjacent conductor turns of the winding the resulting frictional work may raise the temperature of the conductor. It has been estimated that temperature increases of a number of degrees are possible where a conductor moves in the order of 0.5 mm. This temperature increase is sufficient to exceed locally the critical temperature and initiate a disturbance which may propagate throughout the coil depending upon heat transfer characteristics of the winding. Accordingly, it is desirable to constrain the windings to avoid any such movement. Historically the method of achieving this has been to impregnate the complete winding or winding pancakes.
Recently it has been proposed that each conductor or possibly several conductors of the coil winding be mounted in a channel provided in a metal or insulator plate. These plates were to be longitudinally located along the MHD conduit. The channels would be designed to constrain the relative and absolute movement of individual conductors to substantially reduce any localized frictional heating. While the use of such plates would provide rigid constraint against movement they would substantially increase the overall size and weight of the MHD magnet assembly. Such increases are particularly important where the magnet must be superconducting, requiring a dewar enclosure which must enclose the magnet and the external containment structure which contains the transverse loads created by the magnetic field.
The three basic Lorentz forces produced by and which act upon the windings in an MHD magnet are the transversely repulsive force (F.sub.(y)) and laterally attractive force (F.sub.z) and the axially repulsive force (F.sub.x). The most important force in the consideration of MHD magnetic design is the transverse repulsive forces. This force is substantial and requires a superstructure for containment of the winding against movement away from the axis of MHD channel. The axial repulsive force as well as the laterally attractive force, on the other hand, normally can be carried by the combination of the windings themselves and any external containment structure designed to handle and constrain the transverse force. In some cases the laterally attractive force (F.sub.z) can be used to aid in the design of the system embodying the present invention.
Constraint of the transverse forces has been achieved by the use of various external containment structures. For example: ring girders, ring stiffeners, and ring girders with tension rods have been used with circular winding geometries. These same containment structures have also been used with rectangular winding geometries; however, simpler structures have been suggested such as a plurality of beams connected by means of tension rods or plates with shear stops (see, e.g., "Fabrication and Assembly Considerations for a Base Load MHD Superconducting Magnet System," Thome, Pillsbury, Ayers, Hrycaj, IEEE Trans. Vol. MAG 15, January 1979, pages 306-39 309; and "Superconducting Magnets and MHD Test Facility and Base Load Power Plant," Stekly, Thome and Punchard, IEEE Trans., Vol. MAG-13, pages 636-639, 1977). Typically, the structural beams are made of aluminum or stainless steel and are connected across the conduit by means of tension members. Various designs have been utilized to minimize the size and weight of the external containment structure as well as to facilitate fabrication. Fabrication of the magnets is an important design consideration inasmuch as the size of the units for commercial MHD power plants may necessitate that their fabrication be at the use site. The ability to meet precise tolerances is an extremely important consideration in any containment system, but it is particularly important that this precision be obtained in field installation at reasonable costs. Accordingly, it is an object of the present invention to provide a containment structure which prevents both movement of coils subjected to transverse force (F.sub.y) and relative or absolute movement of the winding conductor. It is a further object to provide a structure which minimizes the size and weight of the containment structure to reduce to as small as size as possible the dewar vessel. Additionally, it is an object of the invention to provide a transverse containment structure which is easily assembled.